Pipeline operators are frequently required to know the location and degree of bends in pipelines. While construction engineering drawings frequently include information as to bends, operators from time to time need to know if changes in a pipeline have occurred, such as can be caused by shifts in the earth due to earth quakes or erosion or by physical contact of the pipeline. Where pipelines lie on the bottom of a river, lake, or ocean channel, the pipelines can be engaged by ship anchors to cause displacement of the pipeline. For these and a variety of other reasons, it is important for pipeline operators to periodically verify the existence of bends in a pipeline. "Bends" refer to changes in direction of a pipeline. Other types of pigs are employed for determining other pipeline characteristics, such as dents in the pipeline wall, constrictions, sidewall openings such as a branch fitting, the occurrence of valves or other apparatuses, and the existence of corrosion. The present disclosure, however, is directed toward a type of pipeline pig specifically intended to provide a record indicating changes in the direction, or bend, in a pipeline.
Pipeline pigs for determining deviations in the interior wall of a pipeline are known as caliper pigs. U.S. Pat. No. 3,755,908 entitled "Pipeline Pig", issued Sep. 4, 1973 is an example of a highly successful type of caliper pig.
Others have suggested bend detector apparatuses for use in pipelines. As an example, U.S. Pat. No. 4,780,962 filed Dec. 5, 1983 and entitled "Pipeline Bend Verification Pig" is an example of one type of apparatus for providing a record of bends in a pipeline.
U.S. Pat. No. 4,930,223 issued Jun. 5, 1990, entitled "Bend Detector Pig" is another example of a type of apparatus usable for indicating changes in a pipeline.
U.S. Pat. No. 4,628,613 entitled "Bend Detector For a Pipeline Pig" issued Dec. 6, 1986 is an additional example of a type of bend detector pig.
These references are indicative of the state of the art of pigs for determining changes in the direction of a pipeline. The present disclosure is an improved pipeline bend detector pig which, unlike other apparatuses of the type illustrated in these prior issued patents, does not require essentially two pig structures coupled together by hinge action or other complicated mechanical apparatus. Instead, the improved bend detector pig of this disclosure is a device in which the occurrence of a bend causes variable resistance elements to be actuated to provide electrical signals that are readily recorded for indicating the occurrence of a bend.